1. Field of the Invention
The present invention generally relates to detection of leakage in tanks that store liquids and, more particularly, to detection of liquid leakage in underground storage tanks.
2. State of the Art
It may be appreciated that detection of liquid leakage in underground storage tanks is difficult, especially when tank volumes exceed several hundred gallons. In such tanks, leaks of a fraction of a gallon per hour may represent only minute changes in the volume of the tanks but, nevertheless, can cause substantial economic los over a period of time. Also, liquid leakage from underground storage tanks can cause groundwater pollution which, in turn, may affect drinking water supplies. Because of threats to drinking water posed by underground tank leakage, numerous environmental standards have been promulgated that, typically, mandate leakage of no more than 0.05 gallons per hour underground from storage tanks containing hazardous liquids. Also, it should be noted that leakage of groundwater into storage tanks can contaminate the contents of the tanks and should also be avoided.
One known method to detect liquid leakage in underground storage tanks relies upon measurements of hydrostatic pressure. According to this method, tanks are filled sufficiently to cause flow into a standpipe, then pressure changes at the standpipe are monitored. In conjunction with such pressure measurement techniques, compensation for temperature effects is normally required. Typically, systems to provide temperature compensation are complicated, time consuming, and somewhat inaccurate.
Another known technique to detect liquid leakage in underground storage tanks involves monitoring liquid levels in the tanks. Such techniques are complicated by the fact that liquid elevations can vary due to factors other than leakage, such as temperature, vibration and, evaporation. Thus, liquid level monitors normally require compensation for thermal and other effects. Here again, such compensation systems are usually complicated and somewhat inaccurate.